1. Field of the Invention
The present invention relates to a method for manufacturing a resin-layer coated toner and a resin-layer coated toner obtained by the same, a developer including the resin-layer coated toner, as well as a developing apparatus using the developer and an image forming apparatus.
2. Description of the Related Art
Conventionally, a surface modification treatment for coating the surface of powder particles with a coating material has been performed in order to improve characteristics of the powder particles such as toner particles.
As a method for the surface modification treatment of the powder particles such as toner particles, a method is known that a mechanical stirring force is applied to the powder particles by a rotary stirring section such as a screw, a blade, or a rotor to fluidize the powder particles in a powder flowing passage and a coating material is ejected from a spray nozzle to the powder particles in a fluidized state.
For example, Japanese Examined Patent Publication JP-B2 5-10971 (1993) discloses a surface modification method of solid particles in which a rotary stirring section is rotated at peripheral speed of 5 to 160 m/sec to fluidize powder particles and a liquid is sprayed from a spray nozzle to the powder particles in a fluidized state to adhere fine solid particles contained in the liquid to surface of the powder particles or to form a film of a coating material contained in the liquid on the surface of the power particles. According to the surface modification method disclosed in JP-B2 5-10971, adhesiveness between the coating material and the powder particles is able to be improved and time required for the surface modification treatment is able to be shortened.
However, the method disclosed in Japanese Examined Patent Publication JP-B2 5-10971 (1993) causes following problems. When the rotary stirring section fluidizes powder particles by applying mechanical stirring forces and a liquid substance containing coating materials is ejected to the powder particles in a fluidized state from a spray nozzle, the liquid substance is gasified inside a powder passage depending on the kinds of the liquid substance. Accordingly, the gasified substance needs to be exhausted to the outside of the powder passage, and without exhausting the gasified substance to the outside, a drying speed of the liquid substance is reduced, thus the powder particles in which an undried liquid substance is remained adhere to other powder particles to generate an aggregate of the powder particles, which causes a problem of the lowered yield of the coating particles.
Furthermore, when the powder particles having undried liquid substance left are present, the powder particles are likely to adhere to an inner wall of the apparatus and there is a possibility that, with the adhered powder particles as a core, other powder particles and coating materials aggregate and grow. When the powder particles and the coating materials aggregate and grow on the inner wall of the apparatus, there causes a problem that the passage for the powder particles to flow becomes narrow enough to prevent isolated flowing of the powder particles, as well as a problem of the lowered yield of the coating particles. It is impossible to solve such problems without stably exhausting the gasified substance to the outside of the powder passage.